Ceiling fans often include a motor for rotating the fan blades as well as a light source for illuminating the space in which the ceiling fan is mounted. In some installations, the ceiling fan may receive a single power feed and a single switch (e.g., a mechanical toggle switch installed in an electrical wallbox) may be used to control the power delivered from an alternating-current (AC) power source to both the motor and the light source. In other installations, the motor and the light source may receive separate power feeds and may be controlled independently by a wall-mounted control device. For example, a wall-mounted dual load control device may comprise a motor drive circuit connected to the motor of the ceiling fan via a first electrical wiring and a dimming circuit connected to the light source of the ceiling fan via a second electrical wiring.
The motor drive circuit may comprise one or more capacitors that may be electrically coupled in series with the motor to adjust the rotational speed of the motor to one or more rotational speeds (e.g., rotational speeds less than a maximum rotational speed). In some cases, the capacitors may be electrically coupled in parallel to provide one or more additional rotational speeds. If the capacitors are coupled in parallel when the voltages across the capacitors have different magnitudes, acoustic noise may be generated in the load control device (e.g., due to a large circulating current being generated in the capacitors), which can be bothersome to a user of the load control device. In addition, repetitive occurrences of the large circulating current may damage the capacitors and other electrical components of the load control device.
Some wall-mounted dual load control devices include digital control circuits (e.g., a processing circuit, such as a microprocessor) for controlling the motor drive circuit and the dimming circuit (e.g., using a phase-control dimming technique) and/or for providing advanced features or feedback to a user. Such wall-mounted dual load control devices typically each include a power supply for generating a supply voltage for powering the processing circuit. The power supply may be coupled in parallel with the dimming circuit and may be configured to conduct current through the light source to generate a direct-current (DC) supply voltage when a controllably conductive device of the dimming circuit is non-conductive each half-cycle of the AC power source. Since it may be undesirable to conduct current through the motor load when the motor is off, the power supply may be configured to conduct current through the light source in order to generate the supply voltage. If the light source is removed from the ceiling fan and/or has failed in an open circuit (e.g., is “burnt out” or “blown out”), the power supply will not be able to conduct current through the light source to generate the supply voltage and the microprocessor will be unpowered. As a result, the wall-mountable smart dual load control device become unpowered and thus will not be able to control the power delivered to the motor when the light source is removed from the ceiling fan and/or has failed in an open circuit.